As a technique of a two-dimensional barcode, by which a graphic code is read and information contained in the code is retrieved, there is Japanese Industrial Standards (JIS)X 0510:2004 “Two dimensional symbol—QR Code—”, for example. In addition, a technique for concealing secret information (which is not information to be displayed) into such a two-dimensional barcode is developed. A technique of concealing secret information into such a two-dimensional barcode which has a standard appearance helps to develop application for industries which is demanded handling cryptographic key information or personal information.
[Patent Literature 1] discloses a technique that, in an encrypted matrix two-dimensional barcode composed of black and white pattern, a key for decoding is indicated by deformed cells which have a shape or density different from standard ones.
[Patent Literature 2] discloses a technique that the decryption key code pattern of an encrypted two-dimensional barcode overlaps in a configuration in which the key code pattern is overwritten on a region of at least either one of a data codeword region and a correction codeword region on the generated two-dimensional barcode pattern.
[Patent Literature 3] discloses a technique for generating a code graphics as follow. If the total number of data codewords, which are coded as codewords indicating data is smaller than the predetermined total number of codewords for generating a two-dimensional barcode, a terminator is placed next to the foregoing codeword region. In addition, secret data codes are placed instead of a part of padding codes which should be placed next to the terminator.